The Indian Meteorological Department (IMD) has said that this year, there will be a slight delay in the onset of southwest monsoon over Kerala. The weather agency said in a statement dated May 16, 2023, that the monsoon over Kerala is likely to begin on June 4, 2023. 


However, according to the model error, the monsoon can begin four days prior to June 4, or four days after it.


Monsoon onset over Kerala marks the advance of southwest monsoon over the Indian mainland. This advance is an important indicator that characterises the transition of a hot and dry season to a rainy season. People living in north India can experience relief from scorching summer temperatures as the monsoon progresses northward. 


Normally, southwest monsoon begins over Kerala on June 1, with a standard deviation of about seven days, which means that the season can start seven days before June 1, or seven days after June 1 over Kerala. 


The IMD uses six predictors in its models to determine the onset of southwest monsoon over Kerala. These predictors are minimum temperatures over northwest India; pre-monsoon rainfall peak over southern peninsula; outgoing long wave radiation over south China sea, which refers to the energy emitted by the Earth's surface and atmosphere in the form of thermal infrared radiation, and is a measure of the amount of energy emitted to space by Earth's surface, oceans and atmosphere; lower tropospheric zonal wind over the southeast Indian Ocean; mean sea level pressure over subtropical northwest Pacific Ocean; and upper tropospheric zonal wind over the northeast Indian Ocean.


Last year, the southwest monsoon arrived over Kerala on May 29. In 2021, the season started over the southern state on June 3, and in 2020, on June 1. 


In April, the IMD said that India is expected to receive normal rainfall during the southwest monsoon season despite the probability of the El Niño affecting India this year. 


ALSO READ | Why There Has Been Unseasonal Rain In May, How It May Affect Crops And Inflation


The unseasonal rains which occurred in northwest India, central India and the southern Peninsula from April 27, 2023, to May 3, resulted in the second coldest May Day for Delhi in 13 years. According to experts, the crops that are yet to be harvested, and the plants which are currently being grown, will be affected due to these unseasonal rains. 


The combined influence of the western disturbance and cyclonic circulations resulted in the unprecedented rainfall received in May.